Are you Shadow? We don't have any stuns, and slows don't work (and aren't needed) If you're Shadow, the best way to burst them down is by holding off AA so that you have it ready for transitions, then just MSx3 and MB the two you're assigned to. You want to get them down to just under half health, and then swap. Saving Shadow Orbs can be useful for this aswell, because a 3 orb Mind Blast crit with AA up will easily take away half of their health, maybe even with 2 orbs up.

Oh, and having a Tank standing by the Hammer for stuns can be useful too, just incase you let one slip.

if you give me a full lineup of your raid group i can tell you how to do it. i need to know more than that you have 2 priests though.

some general pointers: holy paladins are great for stunning the sons, they just need to glyph holy wrath and they can aoe stun 2-4 adds usually. hammer of justice is obviously good too. remember to have tanks stun too.

arcane mages are really good for taking down the adds - have them save presence of mind, arcane power and whatever trinket they have. i was able to take down 4 adds by myself when i went on my mage for our alt run last week.

make sure everyone knows what adds they're assigned to before you go. if 1 add is left untouched then its just gonna ram through and hit the hammer in 3 seconds.

dont kill an add before moving on to dps the next one, instead take the add to 50% health, then swap to a new one

EDIT: ok, that setup is pretty good actually. have your prot war shockwave, your blood dk grip an add as far away from the hammer as possible whenever it gets close. you most certainly dont want to respec your arcane mage. they're insanely good for this. your lock can use shadowfury to stun several adds too. if you assign everyone and they follow it corectly, you should have no problems with this

Prot Warrior can use Shockwave to stun multiple mobs that get too close to the Hammer. He can also use Concussion Blow to stun a single mob that gets too close.
Blood DK can Death Grip a mob away from the Hammer if it gets too close.
Holy Pala should Glyph into Holy Wrath, as it allows him to AoE stun Elementals that get too close. He can also use Hammer of Justice to stun a single mob that gets too close.

If they do that and the rest of your group just focusses on nuking down the Sons of Flame, you shouldn't have any problem at all.

Oh, and set markers around the edge of the platform to make it easier to assign DPS to the Sons of Flame. Makes it a lot easier for people to call "I'm on green" for example.

not the greatest of groups dps wise, most pull around 20k average
so far what ive got is having the lock use felguard or go destro
hunter getting a wasp
mage going frost or fire

sons of flame phase is where we are dieing, we rarely get past it at all

Prot warrior can stun 2 sons for few seconds.
Holy pala with something glyphed (only heared about it from raid chat) can stun some.
Feral has a stun too. Even if he has to switch bear and use the bear stun.

You've got no stun, so assuming you're talking about bursting them down as shadow:

Drop mindblast from your casting just prior to the transition phase so you'll have 3x shadow orbs going in.

Hit it with the 3x orb'd Mindblast -> SW death -> mindspike till you can mindblast again.

Once you've got it to 50% you can use a more normal rotation & it'll be moving forward at a crawl anyway, but until you've got it properly slowed pretend you're a mindspiker in PVP. I suspect your problem is that your group is thinking in terms of sustained max dps rather than burst max dps. If necessary, assign everyone a specific add to deal with.. the arcane mage should be able to burst at least couple to 50% solo easily.

PS. and the reason I say SW death before mindspiking is cos that way the damage happens instantly when you push the button, not 1.5s after you push the button.

In our 10 man, I'm holy and usually just Mind Spike spam ones that are the most threatening. I target swap at least twice per Sons.
Our resto druid tries a feral charge, but it misses often enough where can't rely on it.
Our holy paladin has a useful stun, but it can miss easily as well.

The three of us DPS Sons as well, and I always do the most damage, usually about 150k total for both Sons phases which is more than the other two can do combined.

In our 10 man, I'm holy and usually just Mind Spike spam ones that are the most threatening. I target swap at least twice per Sons.
Our resto druid tries a feral charge, but it misses often enough where can't rely on it.
Our holy paladin has a useful stun, but it can miss easily as well.

The three of us DPS Sons as well, and I always do the most damage, usually about 150k total for both Sons phases which is more than the other two can do combined.

A bunch of people have said that your prot warrior can use shockwave and conc blow to stun, but make sure he doesn't forget about charge and intercept. Both of those have stuns associated with them. You prot warrior can bounce around get plenty of stuns out.